Organopolysiloxane coating compositions

ABSTRACT

Fast-curing resin compositions for coating metal surfaces are described. They comprise a high molecular weight epoxy resin, an etherified resol phenolic resin, a silicone fluid and an organopolysiloxane release resin, with an zinc-iron organometallic curing agent and a solvent. In addition to curing rapidly (one minute or less), the resin compositions are flexible and metal sheets coated therewith can be pressed or bent into various shapes and forms without the resin coating cracking or chipping.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of Ser. No. 271,219 FiledJune 8, 1981.

BACKGROUND OF THE INVENTION

Silicone resin compositions have been described which are particularlyapplicable as release coatings for baking utensils. See for example theMerrill et al U.S. Pat. Nos. 3,786,015, 3,925,276 and 4,028,339. Thesepatents describe silanol-containing silicone resin compositions whichare particularly applicable as release agents for cooking and bakingutensils. Such coating compositions, however, require extensive heatcuring at relatively high temperature for an extended period of timeafter application to a metal surface. See for example U.S. Pat. No.4,028,339 (col. 5) which describes the curing of a silanol-containingsilicone resin composition at 425° F. for 45 minutes after applicationto tin-coated steel surfaces. Moreover, such silicone compositions arenot particularly flexible and cannot be applied to metal sheets whichare thereafter drawn and shaped into cooking utensils such as cups, pansand the like.

OBJECTS OF THE INVENTION

It is an object of this invention to provide silicone coatingcompositions which cure rapidly on the surfaces of metal objects andutensils with little or no post heating. It is a further object of thisinvention to provide silicone coating compositions which are flexible atambient temperature and can be applied to metal surfaces which canthereafter be formed and shaped into various cooking utensils andsimilar objects without the resin coating cracking or chipping from themetal surface. It is a further object to provide silicone coatingcompositions which can be applied to metal sheets which are drawnthereafter without the coating composition cracking or breaking awayfrom the metal surface. These and other objects are apparent from andare achieved in accordance with the following disclosure.

SUMMARY OF THE INVENTION

We have discovered that silicone compositions comprising anepoxy-phenolic resin in high boiling solvent which contains acombination of a silanol-containing silicone releasing agent, a siliconefluid and a zinc and/or iron organometallic curing catalyst formcoatings which are rapidly cured in very short time-temperature cycles.These resin formulations can be readily applied to metal surfaces toform thin flexible films which provide excellent release properties forbaked goods.

The resin coating, which can be applied directly to any metal surfacesuch as steel, tinmill black plate, tin-free steel, aluminum, tinplateand the like, comprises a bisphenol-epichlorohydrin polymer of molecularweight in the range of 50,000 to 200,000 dissolved in high-boilingsolvent such as a Cellosolve ester or a high-boiling ketone such asisophorone, combined with an etherified resol bisphenol-epoxy resin, andcontaining a combination of silicones comprising a silanol-containingorganopolysiloxane resin and an alkylphenylsiloxane fluid. The siliconesand combinations thereof are described in U.S. Pat. Nos. 4,028,339 and3,786,015, the disclosure of which is incorporated herein by reference.

While silicone resin combinations are known to be release agents forfood products, the formulations thereof described in prior patents havecertain disadvantages. They must be cured at relatively high temperaturefor rather long periods, and the cured coatings are relativelyinflexible so that coated metal strips cannot be drawn or bent withoutcracking or destroying the coatings. In contrast, the formulationsdescribed herein can cure rapidly at ordinary temperature and theresulting coatings, when applied to metal sheets, can be bent, drawn andpressed into desired shapes without the coating cracking or beingdeformed. These silicone formulations have obvious advantages over thoseof the prior art.

GENERAL DESCRIPTION OF THE INVENTION

This invention is a coating composition for metal surfaces whichcomprises a combination of constituents, as follows:

(A) A high molecular weight phenolic-epoxy resin, preferably a bisphenolA-epichlorohydrin resin, although equivalent epoxy resins are alsosuitable. This resin constitutes about 10% to 25% of the total weight ofthe composition, and has a molecular weight in the range from 50,000 to200,000.

(B) An etherified resol-type phenolic resin, preferably abisphenol-formaldehyde resol resin produced from bisphenol (1.0 mole)and 37% aqueous formaldehyde (1.5 moles) in the presence of anFDA-conforming basic catalyst, such as barium hydroxide. This resinconstitutes a minor proportion of the composition, about 1% to 3% byweight.

(C) A silicone fluid composed of a mixture of methylphenylsiloxanes,dimethylsiloxanes and diphenyldimethylsiloxanes. This fluid makes upabout 1% to 3% of the composition weight.

(D) An organopolysiloxane release resin containing silanol groups, asdescribed in the Merrill U.S. Pat. No. 4,028,339. It usually forms 12%to 20% of the composition weight. The quantity of the silicone releaseresin can be varied from twice to fifteen times the weight of thesilicone fluid (component C); preferably the ratio is 5:1 to 10:1.

(E) A zinc and/or-iron curing catalyst in amount sufficient to cure thecomposition at room temperature. The preferred catalysts are zinc oriron salts of organic acids, such as aliphatic and cycloaliphatic acidscontaining six to twenty carbon atoms. Preferred catalysts are iron andzinc octoates and naphthenates, in conventional solvents. The amount ofcatalyst metal in the formulation, based on the total weight of thesilicones (C and D) is 0.01% to 0.25% zinc and 0.001% to 0.12% iron,depending on cure conditions. By using the zinc octoate and ironnaphthenate as catalysts, we are able to provide a single package, thatis, the catalysts incorporated into the coating at the time ofmanufacturing of the coating. This provides a five-month stability withno adverse effects where cure and food release properties are concerned;but more important, the release properties are enhanced ten-fold.

(G) Suitable solvents for the constituents and the final composition.

The coating composition can comprise the six components described aboveand can be applied directly to metal surfaces and cured thereon in timetemperature cycles of 1/2 to one minute at 450°-490° F. It ispreferable, however, to combine the polymer constituents (A through D)and appropriate solvents in one solution and maintain the organometalliccatalyst in a second solution. The catalyst solution can then be admixedwith the polymer solution prior to application.

A less expensive coating procedure, which reduces the amount ofexpensive organopolysiloxanes required to cover a given area, comprisesthe application of a base coat to the metal surface, followed byapplication of the coating composition described above. The base coat isan epoxy-phenolic resin of the general formulation described hereinwithout the silicone components, with a colored pigment if desired, inan organic liquid carrier. It is coated on the metal surface, thecarrier evaporated and the coating cured. Thereafter the coatingcomposition described above is applied and cured in a very shorttime-temperature cycle. By use of the base coat, the quantity ofexpensive ingredients for a given area is reduced.

In addition to the components (A to E) described above, other materialsmay be included in the coating composition to achieve certain desirableeffects. For instance, silicones may be added for flow control of thecompositions to provide smooth coatings on surfaces. Plasticizers may beincluded to improve film continuity and make the cured coating moreflexible in the pan-forming operation. Other phenolic resins may beincorporated in the coating to resist the adverse effects of detergentsin pan washing.

EXAMPLE 1

A flexible silicone top coating of wide applicability is produced fromthe following materials:

    ______________________________________                                        High molecular weight    464 lbs.                                             bisphenol A-epichlorohydrin                                                   resin (min. mol. wt. 50,000;                                                  hydroxyl no. 0.35; 32% solids in                                              Cellosolve ester)                                                             Isophorone               60 lbs.                                              Etherified resol         18 lbs.                                              bisphenol-epoxy resin (50% solids                                             in butanol; Araldite DP-139)                                                  Mixture of methylphenylsiloxanes,                                                                      16 lbs.                                              dimethylsiloxanes and diphenyl-                                               dimethylsiloxanes (G.E. silicone                                              fluid 81950)                                                                  Silanol-containing       144 lbs.                                             methylphenylpolysiloxane resin                                                (Example I, Pat. No. 4,028,339)                                               Hydrocarbon solvent      54 lbs.                                              Xylene                   54.6 lbs.                                            ______________________________________                                    

The etherified resol bisphenol-epoxy resin is dissolved in theisophorone and the resulting solution is mixed into the high molecularweight bisphenol A-epichlorohydrin resin. Then the two siloxanecomponents are added followed by the hydrocarbon solvent and xylene.

To the resulting resin solution are added 2 lbs. of zinc octanoate and1.5 lbs. of iron naphthenate in 6 lbs. of aliphatic hydrocarbon solventand 5.6 lbs. of xylene. The resulting solution is a silicone coatingcomposition which cures rapidly at moderate temperature on metalsurfaces and has a pot life of several days. Tinplate coated with thiscomposition can be drawn and shaped into muffin tins without rupturingthe resin coating and the muffin tins provide excellent release of bakedgoods.

EXAMPLE 2

A clear flexible silicone top coating of wide applicability was producedin accordance with the following formula:

    ______________________________________                                        High molecular weight    464 lbs.                                             bisphenol A-epichlorohydrin                                                   resin (min. mol. wt. 50,000;                                                  hydroxyl no. 0.35; 32% solids in                                              Cellosolve ester)                                                             Isophorone               60 lbs.                                              Butyl Cellosolve         45 lbs.                                              Etherified resol         10 lbs.                                              bisphenol-epoxy resin (50% solids                                             in butanol) Defoaming agent                                                   (25% Modaflo, Monsanto)                                                       Mixture of methylphenylsiloxanes,                                                                      10.5 lbs.                                            dimethylsiloxanes and diphenyl-                                               dimethylsiloxanes (G.E. silicone                                              fluid 81950)                                                                  Silanol-containing       144 lbs.                                             methylphenylpolysiloxane resin                                                (Example II, Pat. No. 4,028,339)                                              Silicone flow control agent                                                                            10 lbs.                                              (20% solution of Byk 300 of                                                   Byk-Mallinckrodt)                                                             Hydrocarbon solvent      54 lbs.                                              Xylene                   54.6 lbs.                                            Zinc octoate (8% solution in                                                                           4 lbs.                                               xylene)                                                                       Iron naphthenate (6% solution in                                                                       4 lbs.                                               xylene)                                                                       ______________________________________                                    

The etherified resol bisphenol-epoxy resin was dissolved in theisophorone and the resulting solution was mixed into the high molecularweight bisphenol A-epichlorohydrin resin. Then the two siloxanecomponents were added, followed by the hydrocarbon solvent and xylene.

To the resulting resin solution was added the zinc octanoate and ironnaphthenate in xylene. The resulting formulation was a silicone coatingcomposition which rapidly cured on metal surfaces (60 seconds at a metaltemperature of 450° F.) and had a pot life of several months. Tin millblack plate coated with this composition can be drawn and shaped intomuffin tins without rupturing the resin coating and the resulting muffintins provide excellent release of baked goods. The release properties ofthis formulation were enhanced ten-fold over those of Example 1 of ourapplication Ser. No. 271,219 filed June 8, 1981.

We claim:
 1. A fast-curing resin coating composition comprising:(i)10-25 parts of an epoxy resin of molecular weight 50,000 to 200,000,(ii) 1-3 parts of an etherified resol phenolic resin, (iii) 1-3 parts ofa silicone fluid comprised of methylphenylsiloxanes, dimethylsiloxanesand diphenyldemethylsiloxanes, (iv) 12-20 parts of an organopolysiloxanerelease resin prepared by(a) agitating a mixture comprising (A) anorganohalosilane blend consisting essentially of about 60 mole percentmethyltrichlorosilane, about 35 mole percent phenyltrichlorosilane, andabout 5 mole percent dimethyldichlorosilane, (B) water, (C) acetone, and(D) a water-immiscible organic solvent, wherein there is present byweight in said mixture per part by weight of (A), about 1.7 to about 10parts of (B), about 0.2 to about 5 parts of (C), and about 0.3 to about5 parts of (D); and (b) separating the organic solvent solution of (F)from the resulting hydrolysis mixture of a step (i), wherein (F) is asilanol-containing organopolysiloxane resin having an average ratio ofabout 1.05 organic radicals per silicon atom, (vi) a catalytic amount ofan zinc-iron organometallic curing agent, in a (vii) suitable solvent,all of the parts being parts by weight.
 2. A resin composition accordingto claim 1 wherein the high molecular epoxy resin is a bisphenolA-epichlorohydrin resin.
 3. A resin composition according to claim 2wherein the etherified resol phenolic resin is a bisphenol-formaldehyderesin.
 4. A resin composition according to claim 3 wherein thesilanol-containing organopolysiloxane release resin is produced fromphenyltrichlorosilane.
 5. A resin composition according to claim 4wherein the organopolysiloxane release resin is produced from a silaneblend of methyltrichlorosilane, phenyltrichlorosilane anddimethyldichlorosilane.
 6. A resin composition according to claim 5wherein the silanol-containing organopolysiloxane release resin isproduced from a silane blend of 526 parts of methyltrichlorosilane, 436parts of phenyltrichlorosilane and 38 parts of dimethyldichlorosilane.